Hierarchical functionalized 3D-connected carbon film with decoupled Fe species for highly efficient Li-O2 batteries

Lithium‑oxygen (Li-O 2 ) batteries have demonstrated extremely high theoretical energy density, making them promising as an alternative energy storage for lithium-ion batteries. However, the sluggish kinetics of discharge and charge during the operation of Li-O 2 batteries have led to low round-trip efficiency, increased parasitic reactions, and short cycle life. Therefore, it is crucial to develop highly efficient electrocatalysts to facilitate the discharge and charge processes of rechargeable Li-O 2 batteries with high performance. Herein, a facile and cost-effective synthesis of the free-standing hierarchical functionalized 3D-connected carbon film with decoupled Fe species has been investigated for Li-O 2 batteries. We identify that the carbonization atmosphere plays a crucial role in generating hierarchical structure, and the film generated from acetylene (Fe SA /NCF-CNT/Fe 3 C) shows decoupled Fe species dispersed in different regions in the hierarchical structure. Through DFT calculations and monitoring of the Li 2 O 2 formation and decomposition, we demonstrate that the single Fe atoms scattered on the N-doped backbone facilitate the one-electron reduction of oxygen while the superoxide tends to migrate to the surface of encapsulated Fe 3 C to form Li 2 O 2 film. Benefiting from the decoupled process and synergistic effect between the Fe species, Fe SA /NCF-CNT/Fe 3 C exhibits catalytic capabilities for oxygen reduction and oxygen evolution reactions in Li-O 2 batteries, leading to low overpotentials (as low as 3.5 V), high reversible capacities (7.4 mAh cm −2 ), and prolonged cycle life (>3250 h). This methodology provides a large-scale production strategy to prepare binder-free catalysts for highly efficient Li-O 2 batteries for potential future industrial applications. • Hierarchical 3D carbon film with decoupled Fe was made via breath-figure, phase-control polymerization, and carbonization. • Single Fe atoms initiate O 2 reduction to superoxide, which forms film-like Li 2 O 2 on CNTs with Fe 3 C nanoparticles' assistance. • Interconnected pores and stuffed CNTs enlarge surface area for film-like Li 2 O 2 , boosting capacity. • The synergistic effects between the decoupled Fe species result in a significant reduction in charge potential to 3.6V. • Li-O 2 batteries with this electrode show high stability, operating over 3250 h without deterioration.